Arginine vasopressin (AVP) is a neurohypophyseal neuropeptide produced in the hypothalamus, and is involved in many biological processes in the circulatory system, the peripheral nervous system (PNS), and the central nervous system (CNS). In particular, AVP acts as a neurotransmitter in the brain. Several pharmacologically significant vasopressin receptor subtypes, including vasopressin V1a, V1b, and V2, have been identified. Such vasopressin receptors are involved in several psychiatric, psychological, and behavioral disease states including depression, anxiety, affective disorders, and stress, as well as non-opioid mediation of tolerance for pain. Vasopressin receptors are also involved in a number of metabolic processes including water metabolism homeostasis, renal function, mediation of cardiovascular function, and regulation of temperature in mammals.
For example, AVP plays an important role in the onset of depression, one of the most common of the serious CNS disorders. Among the potential targets for treating depression is the hypothalamic-pituitary-adrenal-axis (HPA axis), which is perturbed in many depressed patients, as well as in stress-related affective disorders (see, Scott and Dinan, 1998; Serradiel-Le Gal et al., 2002, the disclosures of which are incorporated herein by reference). Normalization of HPA axis function appears to be a prerequisite for sustained remission of depressive symptoms when medication is used (see, Steckler, et al., 1999, the disclosures of which are incorporated herein by reference).
One of the signs of major depression is an elevated level of cortisol and ACTH associated with dysregulation of the HPA axis (see, Owens and Nemeroff, 1993; Plotsky et al. 1998, the disclosures of which are incorporated herein by reference). Corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) are the two main ACTH secretagogues, and recent preclinical and clinical studies have shown that AVP is important in mediating ACTH release during chronic psychological stress (see, Scott and Dinan, 1997, 1998, the disclosures of which are incorporated herein by reference). AVP is made in neurons localized to the paraventricular nucleus of the hypothalamus, and activation of these neurons causes the release of AVP into the portal circulation of the median eminence. However, the cortisol response to psychological stress appears to be regulated by AVP, but not by CRH in anxious healthy human volunteers (see, Boudarene et al., 1999, the disclosures of which are incorporated herein by reference). Chronic psychological stress accompanied by dysregulation of the HPA axis may contribute to the etiology of affective disorders. It has been found that many patients with major depression show elevated levels of AVP that decline as the mental illness improves (see, van Londen et al., 1997 & 2000, the disclosures of which are incorporated herein by reference).
AVP is also transported to the anterior pituitary where it can stimulate ACTH release by interacting with a V1b receptor on the cell membranes of corticotrophs. For example, rats selectively bred for high anxiety-related behavior show dysregulation in this HPA axis. Treatment with a V1b receptor antagonist can abolish CRH-stimulated ACTH secretion, demonstrating a shift in ACTH regulation from CRH to AVP (see, Keck et al., 1999, the disclosures of which are incorporated herein by reference). The presence of V1b receptors in several regions of the rat CNS and mouse CNS has also been demonstrated. It is therefore believed that V1b antagonists that penetrate the CNS may have greater therapeutic potential for stress-related affective disorders. Currently there are no vasopressin antagonists that are able to cross the blood brain barrier (Serradeil-Le Gal et al. 2002). There is also preclincial and clinical evidence that vasopressin, acting through a V1b receptor, contributes to a subtype of major depression associated with chronic stress and dysregulation of the HPA axis (see, Boudarene et al., 1999; Griebel et al., 2002; Scott and Dinan, 1997, 1998, the disclosures of which are incorporated herein by reference).
It has been reported that cardiovascular disease accounts for the largest cause of hospitalizations in individuals aged 65 years and older. It has been demonstrated that AVP contributes to the pathophysiology and progression of heart disease, including congestive heart, failure (see, Schrier & Abraham “Hormones and hemodynamics in heart failure,” N. Engl. J. Med. 341:577-585 (1999); Thibonnier “Vasopressin receptor antagonists in heart failure,” Curr. Op. Pharmacology 3:683-687 (2003); Lee et al., “Vasopressin: A new target for the treatment of heart failure,” Am. Heart J. 146:9-18 (2003), the disclosures of which are incorporated herein by reference). In addition, the coordinated physiology of the renal/cardiovascular systems contributes to normal cardiac performance and homeostasis. Thus, AVP also plays an important role in water and electrolytic balance, regulation of blood volume, vascular smooth muscle tone, and cardiac contractility and metabolism. Each of these are major factors affecting the performance of the heart and its ability to meet the demands of the body. AVP affects all of these factors, in particular through activation of V1a and V2 receptors. Vasopressin V1a receptors are localized to vascular smooth muscle and cardiomyocytes, promoting vasoconstriction and myocardial cell protein synthesis and growth, respectively. Vasopressin V2 receptors are localized to the collecting ducts of nephrons in the kidney promoting free water reabsorption. Small changes in plasma osmolarity are sensed by receptors in the hypothalamus, which regulates the neurosecretory release of AVP from the pituitary gland. With osmotic stimulation, plasma AVP levels can rise from a basal level of 3-4 pg/ml to 9-10 pg/ml. These modest changes in AVP neurohormone level, in concert with the renin-angiotensin-aldosterone system, regulate the day-to-day water and electrolyte balance in healthy subjects.
However, it has been reported that the role of AVP in the cardiovascular physiology of healthy subjects is minimal, and for those persons, supraphysiological doses of neurohormone are needed to affect blood pressure, cardiac contractility, and coronary blood flow. In contrast, AVP plays a substantive role in patients with heart failure. For example, it has been observed that basal plasma levels of AVP are elevated in patients with heart failure as compared to healthy controls, particularly those that also present with hyponatremia (see, Goldsmith, “Congestive heart failure: potential role of arginine vasopressin antagonists in the therapy of heart failure,” Congest, Heart Fail. 8:251-6 (2002); Schrier and Ecder, (2001), the disclosures of which are incorporated herein by reference). Further, the impaired water diuresis in congestive heart failure (CHF) patients leading to increased blood volume, hyponatremia, edema, and weight gain, is linked to AVP. With heart failure, elevations in plasma AVP lead to increased peripheral vascular resistance and pulmonary capillary wedge pressure while reducing cardiac output and stroke volume. Further, additional evidence suggests that AVP contributes to the hypertrophic myocardium characteristic of the failing heart (see, Nakamura et al., “Hypertrophic growth of cultured neonatal rat heart cells mediated by vasopressin V1a receptor,” Eur J Pharmacol 391:39-48 (2000); Bird et al., “Significant reduction in cardiac fibrosis and hypertrophy in spontaneously hypertensive rats (SHR) treated with a V1a receptor antagonist,” (abstract) Circulation 104:186 (2001), the disclosures of which are incorporated herein by reference), and cell/molecular studies have demonstrated that it also triggers a signaling cascade that promotes the myocardial fibrosis typically seen with progression of the disease.
Structural modification of vasopressin has provided a number of vasopressin agonists (see, Sawyer, Pharmacol. Reviews, 13:255 (1961)). In addition, several potent and selective vasopressin peptide antagonists have been disclosed (see, Lazslo et al., Pharmacological Reviews, 43:73-108 (1991); Mah and Hofbauer, Drugs of the Future, 12:1055-1070 (1987); Manning and Sawyer, Trends in Neuroscience, 7:8-9 (1984)). Further, novel structural classes of non-peptidyl vasopressin antagonists have been disclosed (see, Yamamura et al., Science, 275:572-574 (1991); Serradiel-Le Gal et al., Journal of Clinical Investigation, 92:224-231 (1993); Serradiel-Le Gal et al., Biochemical Pharmacology, 47(4):633-641 (1994)). Finally, the general structural class of substituted 2-(azetidin-2-on-1-yl)acetic acid esters and amides are known as synthetic intermediates for the preparation of β-lactam antibiotics (see, U.S. Pat. No. 4,751,299).